(Supported in part by ACS PRF28650-AC7 to B. Naumann) The primary focus of this study is to acquire information to apply towards the production of blended polymers with optimal properties and therefore, improved functionality. The materials being studied have a wide range of uses in the biomedical field including the acetabulum in total hip replacement. Other applications include dentures and filling material, bone cement and medical packaging. One ongoing study involves the comparison of various polymers performance in impact energy testing. Samples are also being compared on a morphological basis in order to accurately determine the size distribution of particles over a large range of diameters and to determine the 3-D spatial relationships of the particles in the polymer material. The particles range from 2 micrometers to a few tenths of micrometers. The HVEM is the only instrument that can image this entire range and provide the critical 3-D information. Specimens are prepared by cryosectioning and observed in the HVEM at room temperature. Investigations were made with staining techniques to differentiate the different phases. The stain differential in PS/PB/R706 was excellent after modifying the RuOs4 staining procedure. We are currently analyzing the particle size of this blend.. We also observed that in the blend PMMA/PS/PB, the PMMA component is not compatible with the PB, therefore, R740 is not fully at interface. This result agrees with a previous study. In the PS/PB/Ran 48% polymer blend, it was determined that the Ran 48% is at the interface. Hundreds of stereo images were digitized for analysis at RPI, and two papers have been accepted for publication. Timothy J. Cavanaugh, K. Buttle, J. N. Turner and E. Bruce Nauman (1997) Confirmation of Predicted Polymer Blend Morphologies from Bulk Specimens. Polymer Cavanaugh, T.J., K. Buttle, J.N. Turner and DE.B. Nauman. (1997) The study of various styrene-butadiene copolymers as compatibilizers in bulk blends of polystyrene/ polybutadine. Polymer